Linear position and rotary position magnetic sensors, systems, and methods

ABSTRACT

Embodiments relate to a position sensor comprising a magnetic target. The magnetic target includes a magnetic multipole configured to generate a magnetic field. The magnetic field has three mutually-perpendicular components at a first region. Sensor elements can be configured to measure these field components at the first region. In embodiments, comparing the amplitudes of the components can be used to determine a global position, and the instantaneous values of these components can be used to determine a local position.

REFERENCE TO RELATED APPLICATION

This Application is a Continuation-In-Part of U.S. application Ser. No.14/482,457 filed on Sep. 10, 2014, the contents of which areincorporated by reference in their entirety.

FIELD

Embodiments relate generally to linear position and rotary positionmagnetic sensors, systems, and methods, and more particularly to asingle-chip angle sensors and systems and magnetic targets that generateunique ratios derived from different signal components.

BACKGROUND

In many applications, the rotational speed, position, or angle of ashaft or other rotating component is determined using magnetic fieldsensors. For example, Hall sensors or magnetoresistive sensors (such asGMR, AMR, TMR, etc.) can be arranged on or adjacent to the rotatingcomponent. In off-axis sensing, the rotating component includes amagnetic multipole that has permanently magnetized portions, such thatas the rotating component rotates a sensor positioned off of therotational axis observes fluctuations in the magnetic field strengthand/or direction.

There are many possible axial orientations of the sensor in an off-axissystem. In general, one edge of a sensor die is kept parallel to therotational axis of the rotating component. More particularly, twoprimary orientations are most commonly used for cylindrical, rotatingcomponents such as cam-shafts. In the first, the surface of the die istangential to a cylindrical surface (where the axis of the cylindercoincides with the rotational axis). In the second, the surface of thedie is perpendicular to the cylindrical surface. The magnetic target canbe a diametrically magnetized component that is mounted on the rotatingcomponent, either at a point along the length of the component or elseat an end of the component. Conventional systems measure the absoluterotational position of the rotating component by measuring the magneticfield caused by the multipole at each of several locations.

In similar conventional systems, linear position can also be ascertainedusing multiple sensor dies arranged along a linearly moving magnetictarget.

SUMMARY

Embodiments relate to a position sensor comprising a magnetic targetcomprising a magnetic multipole configured to generate a magnetic field.The magnetic field comprises, at a first region, a first component, asecond component, and a third component, wherein the first, second, andthird components are mutually perpendicular to one another at the firstregion. The position sensor further comprises a sensor die having afirst sensor element configured to measure the first component at thefirst region, and a second sensor element configured to measure one ofthe other components substantially at the first region.

According to another embodiment, a magnetic multipole comprises analternating sequence of magnetic south and north poles arranged along afirst direction arranged such that a magnetic field generated by themagnetic multipole at a first region has a first component, a secondcomponent, and a third component, wherein the first, second, and thirdcomponents are mutually perpendicular at the first region. The magneticmultipole can be arranged along an expected sensor track such that thefirst component has an amplitude that is not uniform along the sensortrack. According to another embodiment, a method of determining aposition of a member that is movable in a first direction comprisesarranging a magnetic multipole along a first direction, the magneticmultipole comprising a plurality of magnetic poles having alternatingpolarity, arranging at least two magnetic sensor elements at a firstregion proximate to the magnetic multipole and spaced apart from themagnetic multipole in a second direction, wherein the second directionis perpendicular to the first direction, sensing a first magnetic fieldcomponent along a third direction, wherein the third direction isperpendicular to both the first and second directions at the firstregion to generate a first signal, sensing a second magnetic fieldcomponent along a fourth direction that is perpendicular to the thirddirection at the first region to provide a second signal, deriving fromthe first signal first information indicative of an amplitude of asignal course of the first magnetic field component and deriving fromthe second signal second information indicative of an amplitude of asignal course of the second magnetic field component, and combining thefirst and second information in order to provide a global position ofthe member.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments may be more completely understood in consideration of thefollowing detailed description in connection with the accompanyingdrawings, in which:

FIG. 1A is a plan view of a magnetic target having an eccentricallymounted magnetic multipole ring, according to an embodiment.

FIG. 1B is a cross-sectional view of the magnetic target of FIG. 1Aalong line 1B-1B, further showing a magnetic sensor element and a sensordie, according to an embodiment.

FIG. 1C is a chart of the radial, axial, and azimuthal field strengthscorresponding to an eccentrically mounted multipole ring, according toan embodiment.

FIG. 1D is a plan view of a magnetic target having an eccentricallymounted magnetic multipole ring of elliptic shape, according to anembodiment.

FIG. 2A is a plan view of a magnetic target having a discontinuousmagnetic multipole, according to an embodiment.

FIG. 2B is a perspective view of a magnetic target and sensor die,according to another embodiment.

FIG. 2C is a chart of the spatial variation of a permanent magnetic ringaccording to an embodiment.

FIG. 2D is a chart of the spatial variation of a permanent magnetic ringaccording to a further embodiment.

FIG. 3 is a cross-sectional view of a magnetic sensor element and sensordie arranged between a magnetic target and shielding, according to anembodiment.

FIG. 4 is a flowchart depicting a method for measuring the absoluterotational position of a magnetic target using a single sensor die,according to an embodiment.

FIGS. 5A and 5B illustrate a linear position sensor and shielding,according to an embodiment.

FIG. 6 is a plan view of a linear position sensor target, according toanother embodiment.

FIG. 7 is a plan view of a linear position sensor target, according toyet another embodiment.

While embodiments are amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Embodiments relate to sensors, systems, and methods for detection ofangle and/or position of components. In various embodiments, permanentmagnet code wheels or strips can be arranged such that as a rotatingcomponent turns, a single off-axis sensor die or chip can be used togather sufficient data to ascertain the rotational position of thatrotating component. In embodiments, this can be accomplished using amagnetic code wheel that is arranged about an eccentric axis, and/or thecode wheel can have an irregular (e.g., elliptical, discontinuous, orother non-toroidal) shape. In other embodiments, a single sensor chip ordie can be used to gather sufficient data to ascertain the position of alinearly-moving target having a magnetic portion that is arranged toprovide a unique magnetic signal as a function of its position.

FIGS. 1A and 1B show magnetic target 100, which can be used to measurethe rotational position of an attached rotating component such as arotating shaft (not shown). Magnetic target 100 comprises first portion102 and permanent magnet ring (PMR) 104. First portion 102 is astructural component that supports PMR 104. PMR 104 and first portion102 are rigidly attached to each other. In embodiments, PMR 104 is anarrangement of multiple magnetic pole pairs which are distributed alonga path 112, e.g. a circular path, an elliptical path, a spiral portionetc. The pole pairs are distributed along the path such that a magneticsouth pole is adjacent to a magnetic north pole and vice versa. In someembodiments, the pole pairs may be distributed regularly along PMR 104.Such distributions may assist in providing an easier calculation of arotating position. In other embodiments, the pole pairs may bedistributed irregularly along PMR 104. Such distributions may increasethe effort of calculation but may on the other hand assist indetermining a unique rotating position for all rotational positions. Insome embodiments, the pole pairs are of equal size and shape. In someembodiments, the pole pairs may have varying sizes or varying shapes orboth.

In the embodiment shown, first portion 102 is a disk, although in otherembodiments first portion 102 could have any other geometry configuredto support a PMR (e.g., PMR 104). In various embodiments, first portion102 can also be configured to mount to a rotating component (not shown),such as a cam shaft. First portion 102 can be mounted, for example byinterference fit or threaded engagement, to co-rotate with such acomponent about a common axis, COR 106. Center of rotation (COR) 106 isthe center of rotation of the PMR 104. In addition COR 106 is also thecenter of rotation for the first portion 102. First portion 102 can be,for example, a ferrous steel disk configured to be mounted to a camshaft or other shafts. PMR 104, as shown in FIGS. 1A and 1B, is atoroidal loop. In some embodiments, all pole pairs are arranged to besubstantially within a plane perpendicular to the axis of rotation, ascan for example be observed from FIG. 1B. In the embodiment shown inFIGS. 1A and 1B, PMR 104 is a permanent magnetic multipole with the polepairs distributed along a circle with inner radius R1 and outer radiusR2. Center of Permanent Magnet (CPM) 108 is the geometric center of PMR104. While PMR 104 may be symmetrical with respect to CPM 108, in otherembodiments PMR 104 may be shaped to be not symmetrical with respect toCPM 108. A plurality of magnetic elements or segments 110 make up PMR,and are permanently magnetized portions. Thus, the magnetic fieldstrength and direction around PMR 104 changes as a function of position.In the embodiment shown in FIGS. 1A and 1B, the direction ofmagnetization of segments of PMR 104 is axial, whereas in variousalternative embodiments segments of PMR 104 could be magnetized in anazimuthal direction, or in more complex arrangements such as Halbachmagnetization. Further, although PMR 104 of FIGS. 1A and 1B is a toroid,in other embodiments PMR 104 could be elliptical, or be irregularlyshaped as described, for example, in the embodiment depicted in FIG. 2A.In some embodiments PMR 104 is positioned along sensor track 112, asdescribed in more detail below. Sensor track 112 is a virtual circlearound the axis of rotation centered in COR 106, the radius of thecircle determined by the radial distance of the sensor to the axis ofrotation. As known to a skilled person sensor track 112 is a virtualtrack which is obtained by kinematic inversion, i.e. assuming therotatable parts to be fixed and the non-rotatable sensor to berotatable. In other words, while the sensor is mounted to benon-rotatable, the various position of the sensor with respect to therotatable parts (such as for example PMR 104) are reflected by assumingthe sensor to be rotatable along the sensor track 112 and the rotatablepart to be fixed. Since PMR 104 is positioned along sensor track 112, aprojection of the sensor track 112 in air gap direction is fully locatedwithin the boundaries of PMR 104. Air gap is the minimum distancebetween the sensor element and PMR 104 and the air gap direction is thedirection in which the minimum distance is obtained.

In FIG. 1A a projection of sensor track 112 is fully encompassed withinPMR 104 although the radial distances R3 and R4 of the boundaries of PMR104 vary. In embodiments, the air gap between a respective sensorelement 114 and PMR 104 is constant in the course of rotation.Embodiments in which the sensor track projection along air gap directionis fully within the boundaries of PMR 104 allow for a constant air gapdistance and thereby to obtain an oscillatory behavior with a constantamplitude of at least one magnetic component along the sensor trackwhile at least one other magnetic component has an oscillatory behaviorwith a varying amplitude along the sensor track due to irregularitiessuch as an eccentricity e (see FIG. 1A) or spiral shape (see FIG. 2A)etc. as will be described later. Distinguished therefrom, sensingsystems in which the air gap changes in the course of rotation typicallydo not allow achieving a constant amplitude of at least one fieldcomponent because the varying radial distance between sensor element andPMR 104 modulates the amplitude for all field components. Sensor element114 is arranged on sensor die 115. Sensor die 115 is a mounted to benon-rotating. Sensor die 115 is positioned in a region in which thereare three components of the incident magnetic field (i.e., axial,azimuthal, and radial) that are mutually perpendicular to one another.At certain rotational positions one or two of these components mayvanish (see FIG. 1C). In various embodiments, sensor element 114 can bea Hall effect sensor element, or a magnetoresistive sensor element. Inembodiments, sensor die 115 can include multiple sensor elements. Forexample, in some embodiments, sensor die 115 can include a sensorelement 114 that is sensitive to magnetic field components along theradial direction (i.e., a direction orthogonal to COR 106). In otherembodiments, sensor die 115 can include a sensor element 114 that issensitive to magnetic field components along the radial direction, aswell as a second sensor element 114 that is sensitive to magnetic fieldcomponents in the axial direction (i.e., parallel COR 106) or theazimuthal direction (i.e., tangential to sensor track 112). Sensor track112 is a track along which the sensor element 114 is configured tomeasure a magnetic field strength and/or direction.

Various distances are referred to herein with respect to FIGS. 1A and1B, including eccentricity e (the distance from COR 106 to CPM 108),reading radius R0 (the distance from COR 106 to sensor track 112), innerradius R1 (the distance from CPM 108 to the inner radial edge of PMR104), and outer radius R2 (the distance from CPM 108 to the outer radialedge of PMR 104). Furthermore, radius R3 is shown as a function of theangle of rotation of magnetic target 100, φ. R3(φ) is the distancebetween COR 108 and the inner radial edge of PMR 104. Likewise, R4(φ) isthe distance between COR 108 and the outer radial edge of PMR 104. Assuch, the cross-section shown in FIG. 1B (parallel to eccentricity e),R3(φ′+180°=R1+e at one side—the side of maximum distance between COR 108and PRM 104 as a function of φ—and R3(φ)=R1−e at the other side—the sideof minimum distance between COR 108 and PMR 104 as a function of φ.R4(φ) is equal to R3(φ) plus the radial width of PMR 104, which is shownas substantially constant in the embodiments depicted in FIGS. 1A and1B.

In the embodiment shown in FIGS. 1A and 1B, eccentricity e issufficiently large that it exceeds the mounting tolerances of PMR 104and sensor element 114. Eccentricity e is also small enough that allrotational positions of sensor element 114 are between radii R3(φ) andR4(φ). That is, during rotation of magnetic target 100 about COR 106,magnetic elements 110 that make up PMR 104 are always positioned alongsensor track 112, which is axially adjacent to sensor element 114. Insome embodiments, the radial width of the PMR 104 may be double theeccentricity e. In other embodiments, the radial width of the PMR mayvary.

Magnetic target 100 is configured to co-rotate with a rotatingcomponent, and to generate a unique magnetic field signal pattern asfirst portion 102 rotates, due to the eccentricity of permanent magnetring 104. FIG. 1A shows magnetic target 100 in plan view, illustratingthe eccentric axis of rotation of permanent magnet ring 104, while FIG.1B is a cross-sectional view of magnetic target 100 along line 1B-1B ofFIG. 1A. Magnetic target 100 of FIGS. 1A and 1B is an embodiment of astructure that can be used in combination with one or more magneticfield sensor elements 114 arranged on a single sensor die or chip 115 toascertain the rotational position of an attached rotating component (notshown). Such rotating components are utilized in a variety ofindustries, including but not limited to automotive and aerospacefields. For example, magnetic target 100 could be mechanically coupledto a cam shaft of an automotive engine. Often, it is desirable to obtainthe rotational position of a part that is located in close proximity tovarious other components of a larger system. As such, magnetic target100 is configured to provide absolute rotational position information.

As magnetic target 100 rotates about COR 106, non-rotating sensorelement 114 can detect a magnetic field strength along any of theradial, azimuthal, and/or axial directions (with respect to thedirection of rotation). Due to the alternating magnetization directionsof magnetic elements 110 in the embodiment shown in FIG. 1A along thedirection of movement, the field strength in each of these directionshas an oscillatory behavior e.g. a sinusoidal component. Depending onthe exact manufacturing technology and magnetization procedure, themagnetization of a single magnetic element 110 may be inhomogeneous.Nonetheless, one can compute the resulting magnetic field by assumingvirtual magnetic charges on the surface and in the volume of PMR 104 ateach magnetic element 110, which are arranged in a north-south polepattern. The field strength in the radial direction additionally variesas a result of the eccentricity e. The radial field strength at thoserotational positions in which the outer radial edge of one of themagnetic elements 110 is adjacent to sensor element 114 is relativelystrong, the radial field strength at those rotational positions in whichthe inner radial edge of one of the magnetic elements 110 is adjacent tosensor element 114 is relatively strong with opposite sign, whereas theradial field strength at those rotational positions in which themagnetic elements 110 are nearly equally distant to both inner and outerradial edges of the magnetic elements goes through zero. For themultipole ring shown in FIG. 1A the magnetic field component pointingfrom a test point towards CPM 108 vanishes if the distance of the testpoint to CMP 108 equals sqrt(R1*R2), which is slightly smaller than(R1+R2)/2.

Various components of a magnetic field incident on sensor die 115 can bemeasured by additional sensor elements that are positioned on sensor die115. For example, as described in more detail below with respect to FIG.4, in some embodiments sensor elements 114 can be arranged on sensor die115 in order to measure magnetic field components in the azimuthal,axial, and/or radial directions. In still further embodiments, fieldgradients along a given direction can be measured by positioning sensorelements 114 configured to measure the field components of the samedirection at various positions arranged along a different direction(e.g., positioning sensor elements 114 configured to sense magneticfield components in the radial direction at multiple positions along theazimuthal direction in order to determine a gradient in the azimuthaldirection of the radial magnetic field component, i.e. dBr/dφ). Axialand azimuthal field components are oscillatory, e.g. sinusoidal, withsubstantially constant amplitudes throughout the entire rotation ofmagnetic target 100. In contrast, the radial field component isoscillatory, e.g. sinusoidal (with the same spatial period as the axialand azimuthal components), but the amplitude of the radial component isa function of the absolute rotational position of magnetic target 100,because the radial distance of the sensing elements to the radial centersqrt(R3(phi)*R4(phi)) varies with rotational position phi. Comparing theradial field component or the amplitude of the radial field component tothe axial or azimuthal field components (or both) or the amplitudes ofaxial or azimuthal field components (or both) can be used to produce asignal that corresponds to the global rotational position of magnetictarget 100. Thereby, we denote A as amplitude of a sine wavef(x)=A*sin(x), and for more general kinds of periodic waveforms wedefine it consistently as A=(max(f(x))−min(f(x)))/2 with x0<x<x0+lamda,whereby lamda is the spatial period of the wave (e.g. lamda is equal tothe length of one north pole and one neighboring south pole of themultipole ring along azimuthal direction). The comparison can be, forexample, division of amplitudes of the two signals (e.g., radialcomponent amplitude divided by axial component amplitude, or radialcomponent amplitude divided by azimuthal component amplitude). In otherembodiments, as described in more detail below, comparison can be afunction of all three components together (e.g., radial amplitudesquared divided by the sum of squares of the azimuthal and axialcomponents). This is e.g. the case if azimuthal and axial componentshave equal amplitudes, because then it becomes very easy to determinetheir common amplitude by sampling azimuthal and axial field componentsat the same location and taking the square root of the sum of squares ofboth: amplitude=sqrt(Bphi^2+Bz^2).

One way to detect the amplitude of a magnetic field component is tosample this field component at two locations x1 and x2. This gives B1 atx1 and B2 at x2. These two locations x1, x2 must be along the directionof movement in a distance which is equal to a quarter of the spatialperiod. In case of FIG. 1A these two locations must be on the readingcircle 112 spaced apart by half of the size of a pole. Then theamplitude is obtained by sqrt(B1^2+B2^2).

These comparisons of amplitudes may provide a global position of themagnetic target 100, to within 360°/N, where N is the number ofpole-pairs in the magnetic target 100. For a local position measurement,the values (rather than the amplitudes) of the radial, azimuthal, oraxial components can be measured. By considering both the global andlocal position outputs, the absolute position of magnetic target 100 canbe ascertained.

Comparing the radial field component to the axial or azimuthal fieldcomponents, rather than to predetermined or historical values, can beused to correct for various offsets and/or errors. For example, thiscomparison can be used to correct for thermal offsets, or for lifetimedrift of the sensor elements. Furthermore, in gradiometric embodimentsthe outputs of two sensor elements arranged to sense a component of thefield can be subtracted in order to cancel out homogeneous backgroundfields. As such, homogenous background magnetic fields need not beactually measured; rather, they are canceled out inherently by thesubtraction of the sensed field components at the sensor elements. Thesensor elements 114 may be provided and arranged in some embodiments tomeasure both, the gradient and absolute value of at least one magneticfield component. It is to be noted that the schemes for determining arotation position described herein by utilizing measured absolute valuesor absolute amplitudes of a magnetic field components can be equallyapplied in a similar manner to measured field gradient values of themagnetic field component or amplitudes of field gradients of themagnetic field components. This is obtained since the gradient of a sinewave is again a sine wave (just shifted by a quarter of its spatialperiod) and the amplitude of a sine wave is linked via a scaling factorto the amplitude of the gradient of this sine wave.

In each of the embodiments described above, and in particular for theembodiment shown with respect to FIGS. 1A and 1B, the system does notdeliver unique magnetic field readings at sensor 114 over the course ofan entire revolution of magnetic target 100. The minimum and maximuminner radial distances (i.e., the extrema of R1) are located a halfrotation from one another, and are associated with the largest radialmagnetic field amplitude. A quarter revolution away of these tworotational positions the sensor track is midway (in plan view) betweeninner and outer edges of magnetic poles and there the radial magneticfield has vanishing amplitude. So the radial magnetic field patternresembles an amplitude modulated signal with maximum amplitude atrotational position phi1 (e.g. in FIG. 1C phi1 is 0° as will bedescribed later on), vanishing amplitude at rotational positionphi1+90°, again maximum amplitude at rotational position phi1+180°,followed by vanishing amplitude at rotational position phi1+270°. Notethat the signal of the radial magnetic field component Br reverses itssign at phi1+90° and again it reverses its sign at phi1+270°. So theradial magnetic field component Br exhibits a phase jump of 180° when itpasses phi1+90° or phi1+270°. Conversely the phases of the signals ofthe other magnetic field components do not change. This is due to thefact that the sensor track passes the radial magnetic center line(=sqrt(R3(phi)*R4(phi))) of the poles which causes to change thedirection of the measured radial field component. Therefore, withrespect to the other two field components, a phase jump of half a periodis observed for the radial field component at ph1+90° and ph1+270°. Thephase shift between the radial field component and one of the two otherorthogonal field components (e.g. in FIG. 1C azimuthal field componentBφ) is +90° for rotational positions between phi1 and phi1+90°, whereasthis phase shift is −90° for rotational positions between phi1+90° andphi1+180°. Thus, the absolute rotational position can be ascertained bythe unique values of amplitude and phase shift in the angular range ofphi1 and phi1+180° provided by sensor element 114. However, atrotational position phi1+181° the sensor detects the same amplitude andphase shift between the radial field component and the one other fieldcomponent as on rotational position phi1+179°. Also at rotationalposition phi1+1° the sensor detects the same amplitude and phase shiftas on rotational position phi1−1°. Thus, when using only the absolutevalues of the two field components an ambiguity is present due to thefact that the spacing between the sensor track and the inner and outeredges of the poles (or at least the closer one of both edges of thepoles) is equal in both rotational positions. Eventually this is due tothe specific geometry (i.e. the specific 180° mirror symmetry of the PMRin FIGS. 1A, 1B. While in the embodiment of FIGS. 1A and 1B the radialfield component is reversed at phi1+90° and phi1+270°, it is to be notedthat in some embodiments the width of the magnetic poles may be suchthat the projection of the sensor track 114 does not cross the polecenter curve in the course of rotation resulting in an amplitudemodulation of the radial field component with no phase jump at 90° and270°. However, the phase jumps assist in determining a global positionas described later on. In some embodiments, the unique values limited toan angular range of 180° provided by sensor element 114 based on theradial position of sensor track 112 on magnetic elements 110 issufficient to determine absolute rotational position, as described inmore detail with respect to FIG. 4. In other embodiments, all threefield components are sensed by sensor elements 114 to uniquely determinethe absolute rotational position over a complete revolution of 360°. Inother embodiments, a gradient and an absolute value of at least onefield component is utilized to determine the absolute rotationalposition over a complete revolution of 360°.

In other embodiments, such as those in which the rotating component canmove over a complete revolution of 360°, discontinuous or irregularfeatures can be incorporated into PMR 104 to measure absolute rotationalposition.

FIG. 1C is a chart of field strength (on the ordinate axis) as afunction of rotational position φ (along the abscissa) for a PMR having15 pole-pairs (i.e., 30 magnetic elements). FIG. 1C shows radial fieldstrength Br, axial field strength Bz, and tangential/azimuthal fieldstrength Bφ for an arrangement like the one shown in FIGS. 1A,B. Forease of description, the maximum field strength for each of Br, Bz, andBφ has been normalized to 1, but it should be understood that in variousembodiments the relative strengths of these components of the overallmagnetic field could differ from one another, depending on the size,orientation, and geometry of the magnetic elements (e.g., magneticelements 110 of FIGS. 1A-1B).

Referring again to FIG. 1C, it can be observed that each of the magneticfield components Bz, Bφ and Br are periodical signals having a periodlength and amplitude. While the periodical signals of all fieldcomponents oscillate at a same frequency, the amplitude of theperiodical signal of the Br field component changes in the course ofrotation from 0 to 360°. In other words, the Br field component isamplitude modulated at a lower frequency than the periodic signal, whilethe Bz and Bφ components are not amplitude modulated. Thus, theamplitudes (signal value from maxima to minima of the periodic signal)of the Bz and Bφ magnetic field components are relatively constant at 1.In contrast, the amplitude of Br is itself sinusoidal, with maxima of 1at φ=0 and φ=180°, and minima of 0 at φ=90° and φ=270°. In otherembodiments the maxima of Br may deviate from 1. For φ between 0 and 90°and between 270° and 360°, Br and Bz are in phase, whereas Br and Bφ areout of phase by a quarter period of the periodic signal. For φ between90° and 270°, Br and Bz are out of phase by half a period of theperiodic signal, whereas Br and Bφ are out of phase by three quarterperiods of the periodic signal. This is due to the fact that the signalof the radial magnetic field component Br is reversed at 90° and againreversed at 270° due to the sensor track crossing the magnetic centerline of the poles as described above.

In other embodiments, Br, Bz, and Bφ need not be sinusoidal. Forexample, with decreased distance between the magnetic target and sensor,each of Br, Bz, and Bφ could have other shapes, such as triangularwaveforms. However, as long as Br, Bz, and Bφ are dependent on theposition of the PMR (or other magnetic structures such as thosedescribed below with respect to FIGS. 5-7), the comparison of thesevalues and/or amplitudes can be performed to determine a global positionof the sensor element.

The comparison between the amplitudes of Br and Bz, or Br and Bφ, can beused to determine rotational position. Notably, in the embodiment shownin FIG. 1C, it is not possible to distinguish from the comparison ofthese amplitudes between φ and 180°+φ.

According to one embodiment, in addition to the comparison of only Brand Bz or only Br and Bφ, a comparison of Br and Bz together with acomparison of Br and Bφ may be used to determine the absolute rotationposition from FIG. 1C. When Br is in phase with Bz, the rotationposition is determined to be closer to 0 than to 180°. If Br is out ofphase with Bz, the rotation position is determined to be closer to 180°than to 0°. Assuming it is determined that the position is closer to 0,in a next step it is determined whether the rotation position is greaterthan 0 or not. To achieve this Bφ is used. It is to be noted that forthe radial field component the symmetry relation Br(φ)=Br(−φ) is validwhile for the azimuthal field component the symmetry relation Bφ (φ)=−Bφ(φ) is valid. In view of this, Bφ can be used to distinguish between φ>0or φ<0 except for Bφ=0. In order to distinguish also for Bφ=0, agradiometer sensor arrangement may for example be provided in which thegradient of Bφ in azimuthal direction (φ-direction) is measured todetermine an absolute rotation position also for Bφ=0 situations. Such agradiometer arrangement may be provided for example by two sensorelements sensitive to Bφ component and placed from each other inazimuthal direction by a distance which is different from the periodlength of the Bφ component. Alternatively it is also possible to place asecond Bφ-sensor at a distance to the first Bφ-sensor, whereby thedistance is different from integer multiples of half a spatial period ofthe Bφ-waveform, because then it is guaranteed that even if one of thetwo Bφ-sensors is at a zero-crossing of the Bφ-waveform, the second oneis at a location with Bφ>0 or Bφ<0. Then the sensor can choose thesensor whose signal is stronger to derive the rotation angle.

Alternative or additional, while in FIGS. 1A-1C the amplitude modulationof the radial field component is symmetric with respect to φ=180°, it isto be noted that non-symmetric amplitude modulations can be provided insome embodiments. FIG. 1D shows an embodiment wherein PMR 104 has anellipsoid shape with CPM 108 being the center of the ellipsoid andeccentric to COR 106. Furthermore, the half-axes 116A and 116B of theellipsoid are provided neither parallel nor perpendicular to a lineconnecting COR 106 and CPM 108. The non-symmetric amplitude modulationbreaks the symmetry relation Br(φ)=Br(−φ) of the radial field componentshown in FIG. 1C and may allow in some embodiments to uniquely determinethe absolute positions by evaluating the amplitude of signals Br and Bzor Br and Bφ. It is to be understood that the schemes described abovewith respect to FIG. 1C can also be applied to non-symmetric amplitudemodulations of the radial component.

In alternative embodiments such as that described below with respect toFIG. 2A, asymmetric magnetic rings can be used that result in uniqueamplitude ratios Br/Bz and Br/Bφ). As shown in FIG. 2A, magnetic target200 comprises first portion 202 and magnetic multipole 204. Center ofrotation (COR) 206 is the center of rotation of first portion 202.Magnetic multipole 204 comprises a series of magnetic elements 210arranged in a loop. Sensor track 212 is a track along which sensorelements (e.g., sensor element 114 of FIG. 1B) are configured to measurea magnetic field strength in the radial direction (i.e., parallel to thedirection of reading radius R0). Furthermore, one or both of the axialand azimuthal field components can be measured at substantially the sameposition by arranging further sensor elements on the same sensor die(e.g., sensor die 115 of FIG. 1B). Referring again to the embodimentshown with respect to FIG. 2A, magnetic multipole 204 is shaped as aspiral, with a discontinuity 205 where the two ends of the spiral meet.Because magnetic multipole 204 is not symmetric about any bisectionpassing through COR 206, the absolute rotational position of magneticmultipole 204 can be ascertained throughout the rotation of firstportion 202 by combining the outputs of the various sensor elements ofthe same sensor die.

In the embodiment shown in FIG. 2A, radii R3 and R4 are a function ofthe angle φ at which magnetic target 200 is rotated, while readingradius R0 is still constant (due to a fixed distance between COR 206 anda sensor element similar to sensor element 114 of FIG. 1B). The radiiare related to one another:R3(φ)<R0<R4(φ);andR4(φ)−R3(φ)=W,where W is a constant.

In practice, it is often desirable to add a design tolerance ε, suchthat sensor track 212 is positioned radially at least ε away from R3(φ)and R4(φ). In this way, even despite placement tolerances of the sensorelement and/or magnetic elements, the sensor element will be arranged ina region with a meaningful magnetic field throughout the complete rangeof φ. For example, 75% of the radial width W could be configured to beadjacent to the sensor element during the rotation of magnetic target200, with the remaining 25% used as a guardband for assembly tolerances.The mean radius of the magnetic multipole 204, (R1(φ)+R2(φ))/2, islinear with respect to φ. Furthermore, the radial width W of magneticmultipole 204 is constant with respect to φ. In alternative embodiments,the radial width W or the mean radius could be a function of φ, andeither of them could be irregular or discontinuous. With continuingreference to the embodiment depicted in FIG. 2A,(R3(φ)+R4(φ))/2=R0+(W×x/2)(φ/360°);orSqrt(R3(φ)*R4(φ))=R0+(W×x/2)(φ)/360°),where x is a constant, such as a value between 0 and 1. In oneembodiment, x is about 0.75. As described in more detail with respect toFIG. 4, magnetic target 200 can be used to generate a unique rotationalposition reading for an attached rotating component, using a singlesensor die or chip.

FIG. 2B is a perspective view of another embodiment of a magneticportion 204B and sensor die 214. In the embodiment shown in FIG. 2B,magnetic portion 204B is arranged with its major surface facing radiallyoutward from the COR 206B. Due to the axial offset (axial position ofrelative to center position) of the strip during rotation, the variousfield components (radial, axial, and tangential) will vary in magnitudeduring rotation such that comparison of their amplitudes can be used toascertain a global position, whereas the instantaneous values can beused to determine a local position. System 200B shown in FIG. 2B hasdiscontinuity 205B. As such, the magnetic field generated by magneticportion 204B is unique about its entire 360° rotation.

It is to be noted that in the embodiment of FIG. 2A, the air gapdirection is parallel to the axial direction and the radial position ofthe poles varies to provide the amplitude modulation. In FIG. 2B, theair gap direction is in radial direction and the position of the polesvaries in axial direction to provide the amplitude modulation. In otherwords, a spatial variation of the PMR 104 to provide the amplitudemodulation is in a direction perpendicular to the air gap directionwhich allows keeping the air gap constant throughout the rotation. Forthe radial position variation of FIG. 2A and the axial positionvariation of FIG. 2B, an offset to a reference position (such as anoffset to the minimum position) constantly increases with increasingazimuthal angle φ with a discontinuity after one rotation. FIG. 2C showsas an example of a linear increase from φ=0° to φ=360° for a reducednumber of pole pairs. In other embodiments, such as shown in FIG. 2D,the offset may increase in a first region and decrease in a secondregion. The absolute value of the gradient of the offset may bedifferent in the first and second regions, i.e. the increase in offsetbetween adjacent pole pairs may be faster than the decrease in thesecond regions or vice versa. It is to be understood that for theembodiments of FIGS. 2C and 2D also gradiometer arrangements may be usedto sense the magnetic field components and to determine the rotationposition. As previously described with respect to alternativeembodiments, magnetic portion 204B can also be configured to rotate witheccentricity about COR 206, such that the radial distance between sensordie 214 and magnetic portion 204B changes. There are other embodimentsbeyond those described with respect to FIGS. 2A and 2B. In alternativeembodiments, for example, the magnetic portion could rotate about COR206B without eccentricity, and could be a helical strip extending in theaxial direction. In such embodiments, the amplitudes of mutuallyperpendicular field components can be compared to one another todetermine a global position (with accuracy depending on the number ofpole-pairs of the magnetic portion) and the local position can bedetermined by observing the magnetic fields in any of the perpendiculardirections.

Various alternative targets can be constructed that generate uniquemagnetic field patterns as a function of φ. For example, the poles(e.g., 110, 210) of the magnet ring or strip need not necessarily beidentical in size or shape. If they are not identical in size, then thenumber of poles can be either even or odd. Furthermore, the thickness ofthe magnetic portions (e.g., 104, 204) could also be varied in the axialor radial directions. One might increase the thickness near the innerdiameter of the ring in order to counter-balance the curvature of thering by putting more emphasis on the inner parts of the ring and pushingthe “magnetic” center of the ring outward. Furthermore, the magneticmultipole may have a shape with inner and outer perimeters beingcircular, and centered on the center of rotation, and yet stillgenerating unique magnetic signal output based on a thickness in axialdirection that varies versus azimuthal position. The thickness of themagnetic multipole can be varied such that at some rotational positionsthe magnetic multipole is thicker near the inner perimeter, whereas forothers (e.g., diametrically opposite positions) the magnetic multipoleis thicker near the outer perimeter. The thicker parts enhance the fieldand pull the “magnetic” center towards the thicker portions, causingmagnetic field differences as a function of rotational angle φ.

FIG. 3 illustrates a sensing system 301 that includes shielding againstboth mechanical damage and electrical interference. The embodiment shownin FIG. 3 includes many of the same components previously described withrespect to FIGS. 1A, 1B, and 2, and like parts are shown with similarreference numbers iterated by factors of 100. In addition to thecomponents previously described with respect to FIGS. 1A, 1B, and 2, theembodiment shown in FIG. 3 includes shielding 316. Shielding 316protects sensor element 314, sensor die 315, and magnetic target 300from mechanical damage due to nearby components within a system. Forexample, in the context of the cam shaft previously described, there areoften nearby elements that generate heat or particulates that couldinterfere with the proper functions of sensor element 314 or damagemagnetic target 300. Furthermore, in some cases, physical contactbetween nearby components can cause damage to sensor element 314, sensordie 315, and/or magnetic target 300. Shielding 316 provides a physicalbarrier to prevent these and other potential unwanted effects.Furthermore, in embodiments where shielding 316 is a material with largerelative permeability, shielding 316 can enhance magnetic field strengthat sensor 314, due to magnetic mirror charges. The mirror charge effectcaused by shielding 316 can further improve magnetic field homogeneityand lead to smaller sensor measurement errors, if the placement ofsensor 314 is not accurate. Shielding 316 can be mounted to co-rotatewith magnetic target 300, or it can remain in a fixed relationship withsensor 314 (i.e., not rotating). If the shielding 316 is fixed to therotating magnet its effect on the magnetic field on the sensor elementsis more accurate because it avoids change of magnetic field on theshield, which might cause hysteresis or eddy currents, however, itincreases the inertia moment of the shaft. So both shields fixed to thesensor or fixed to the rotating magnet have their pros and cons.

FIG. 4 is a flowchart of a method 400 for measuring the rotationalposition of a magnetic target, according to an embodiment.

At block 402, the tangential and/or axial magnetic field components (Bφ,Bz) are sensed. In some embodiments, only one tangential magnetic fieldcomponent Bφ and axial magnetic field component Bz need be sensed. Forexample, at block 402, one could measure only axial magnetic fieldcomponent Bz at sub-block 402 a, or only measure tangential magneticfield component Bφ at sub-block 402 b.

At block 404, radial field component Br is sensed. Radial fieldcomponent Br is sensed using a sensor element positioned on the samesensor die that was used at block 402. As such, the sensed radial fieldcomponent Br is measured at substantially the same position astangential magnetic field component Bφ and/or axial magnetic fieldcomponent Bz sensed at block 402, or within less than a few millimetersof the same position.

Alternatively, sensing tangential, axial, and radial field components atblocks 402 and 404 can comprise measuring a gradient, which is thedifference of the same field component measured at two different spots.A sensor die can contain two or more magnetic field sensor elements eachconfigured to sense the same magnetic field component, such as Br. Inthis way, the gradient of Br along the direction of these two sensorelement positions can be derived. As such, homogeneous magneticdisturbances can be cancelled out, and systematic offset (zero-point)errors of the sensor elements can be cancelled out.

At block 406, radial field component Br is compared to tangentialmagnetic field component Bφ and/or axial magnetic field component Bz.This comparison can take a number of different forms in variousembodiments. For example, in a first embodiment, the comparisoncomprises generating an output of Br/Bφ. In a second embodiment, thecomparison comprises generating an output of Br/Bz. In a thirdembodiment, the comparison comprises generating an output ofBr/sqrt(Bφ²+Bz²). In a fourth embodiment, the comparison comprisesgenerating an output of Br²/(Bφ²+Bz²).

Br and Bz are in phase (i.e. they have a φ-dependence of type cos(N*φ)for N pole-pairs), whereas Bφ is in quadrature with a sin(N*φ)dependence. The three field components can be written as:Br=A(φ)cos(Nφ)Bz=A cos(Nφ)Bφ=A sin(Nφ)with N being the number of pole pairs and φ being the azimuthal angle inradian units. All signals Br, Bz and Bφ have in common that they consistof two factors, an oscillation factor (either sin(Nφ) or cos (Nφ)) andan amplitude factor. The oscillation factor is oscillatory with φincreasing from 0 to 2π. The number of oscillation between 0 and 2πdepends on the number of pole pairs N.

Notably, Br has an amplitude A(φ) that is a function of φ, whereas Bzhas an amplitude A that is constant (or, in some embodiments, a functionof φ with a much weaker dependence on φ). As long as cos(N*phi) isdifferent from 0 the system can compute Br/Bz=A(φ)/A, which is a smoothfunction of φ according to the embodiments shown in FIGS. 1A-1B and 2.From this ratio, the approximate rotational position of magnetic targetcan be determined. While the preceding quotient provides informationregarding whether the sensor is closer the 1^(st), 2^(nd), or N^(th)pole-pair, it does not necessarily provide information regarding whatmagnetic element in particular the sensor is closest to. Thus, thefunction can be used to determine the global angular position (with aresolution of 360°/N) yet not the local angular position (with aresolution better than 360°/N). For the local angular position, variousadditional sensors (such as Bφ and Bz sensors) can be arranged on thesame chip or die as the radial field strength sensor element, to measurethe absolute strength (rather than the amplitude) of the magnetic fieldin those directions.

Therefore, in the first embodiment the quotient contains a cot(N*φ) termwhich must be cancelled by some algorithm in order to determine theratio of amplitude(Br)/amplitude(Bφ), which is related to the globalrotational position of the magnetic target, whereas the second,embodiment from block 406 have only cos(N*φ) terms in numerator anddenominator that cancel out so that the ratio of signals is identical tothe ratio of their amplitudes (unless the numerator vanishes). Havingthe ratio of amplitudes (i.e., either amplitude(Br)/amplitude(Bz) oramplitude(Br)/amplitude(Bφ)), the radial offset of the magnetic fieldsensor from the center of the magnetic track can be estimated and sincethis radial offset is a smooth function of the global angular positionthe sensor can infer if the angular position is roughly near e.g. 0° or90° or 180°. In still further embodiments, at block 406 Bφ and Bz can becompared to one another in order to derive N*φ, which gives the localangular position. This local angular position has an N-foldambiguity—therefore it cannot decide about the global angular position,yet it has a good angular resolution within one pole-pair, i.e. withinan angular range of 360°/N. The sensor system can combine this localangular position obtained by Bφ and Bz with the global angular positionobtained by Br and Bφ or Br and Bz.

In the case of magnetic gradient sensor embodiments, a chip has a mainsurface parallel to the (R,φ)-plane. Two Bz sensor elements are arrangedat identical (R,z)-coordinates, but different φ-coordinates along thesurface of the chip. The system can measure Bz(R, φ1, z) and Bz(R, φ2,z) and compute the difference between those two measurements. Not onlyare background fields cancelled by the subtraction, but also even inthose rotational positions where Bz is zero (such as at the 2*Nzero-crossings along one revolution) the system provides usable data,unlike the Br/Bz embodiment described above. Even if the magneticmultipole is positioned such that the field on one sensor elementvanishes (e.g., Bz(R, φ1, z)=0), the field on the other sensor elementis different from zero as long as the spacing of both sensor elements isless than the azimuthal length of a magnetic pole (=φ*R0/N). If theBz-field varies with cos(N*φ), the gradient of the Bz-field alongφ-direction varies with sin(N*φ).

At block 408, the rotational position of the magnetic target isdetermined. This can be accomplished in two ways, either simultaneouslyor independently. First, the system can detect Bφ and/or Bz, which arehighly oscillatory. Bφ and Bz vary approximately sinusoidally with Nperiods, in those embodiments where the magnetic multipole includes Npole-pairs. This can be used as a speed sensor to give incrementalpulses upon rotation of the magnetic target. Second, the Br-componentcan be used to measure the rotational position, for example if the wheelrotation is slow or at halt or shortly after power-on of the system.

From the above it can be observed that an amplitude of an oscillatorymagnetic field component signal with varying amplitude is determined andset in relationship to an amplitude of an oscillatory signal related toanother magnetic field component. Distinguished from other concepts fordetermining a position, rather than setting the field components inrelation to each other (e.g. Bφ/Br), embodiments described herein firstdetermine an amplitude from each of at least two field components andthen sets the amplitudes in relationship to each other, e.g. bydivision. The amplitude is determined by cancelling the oscillatoryfactor. In a gradiometer system this can be achieved by measuring therespective field component at two different locations along thedirection of the PRM 104. According to some embodiments, the sensortracks of the two sensors forming a gradiometer are the same, with onlythe position being shifted along the sensor track. In other embodimentstwo sensors may be arranged along the direction of the PRM 104 such thatthe sensor tracks are offset to each other but the projection along theair gap direction of both sensor tracks is still encompassed by the PRM104. It is to be noted that the above described gradiometers allowdetermining the amplitudes without actually going through an extrema. Inother non-gradiometer embodiments, the sensor system may measure onlyone field component at only one location. In such systems, the amplitudemay typically be determined after passing an extrema (minimum ormaximum) and then determine the amplitude from the extrema.

FIG. 5A is a plan view of linear position magnetic target 500, whichincludes shielding 516 (in this embodiment, further acting as asubstrate) and a series of magnetic elements, including North Polemagnetic elements 510A and South Pole magnetic elements 510B. In thisembodiment, the sensor track is shown as an x axis, and the centers ofthe magnetic elements 510A and 510B are shown as a dashed line. Itshould be understood that the reference frame shown here is used forconvenience only and should not be construed as limiting. For example,in various alternative embodiments, the sensor track could be anydirection having an x-component, other than the dashed line shownpassing directly along the centers of the magnetic elements 510A and510B. In any direction having an x-component other than along the dashedline, the field strength along the y direction changes sinusoidally as afunction of position. The amplitude of this sinusoidal pattern and itssign (related to the magnetic field components in x or z direction)provide unique values that can be used to determine absolute position.

FIG. 5B is a cross-sectional view of the linear position sensor system501, including magnetic target 500 of FIG. 5A, taken across line 5B-5Bof FIG. 5A. FIG. 5B illustrates a sensor die 515, which includes atleast one sensor element 514, at two positions: x0 and x1. As previouslydescribed, the relationship between two perpendicular magnetic fieldcomponents can be sensed by various sensor elements on sensor die 515,wherein one of the magnetic field components is sinusoidal and varieswith a function of the position of the magnetic target 500 and one ofthe magnetic field components does not.

As shown in FIG. 5B, shielding 516 goes higher than the top surface ofthe magnet (z=0), such as even higher than the sensor element(s) withinsensor die 515. In this way, shielding 516 shields against externalBy-fields, yet the distance between sensor die 515 and shielding 516 islarge enough not to overly affect the Bx, y, z-field components of themagnetic elements 510A, 510B.

FIG. 6 illustrates yet another magnetic target 600, according to anembodiment. In magnetic target 600, the width of the poles 610A, 610Bvaries with the absolute position. Thus, an adjacent sensor element candetermine based on the field strength whether it is nearest a pole(e.g., 610A, 610B) having width W1, W2, W3, or some other width. Thiscan be accomplished by arranging a gradiometer that detects dBy/dy,which depends on the widths of the poles and thus on the globalposition. In some embodiments, the sensor position may be constant inthe center of the poles (with respect to the y-direction).

FIG. 7 illustrates yet another magnetic target 700. In magnetic target700, similar to the embodiment described with respect to FIG. 6, thewidth of the poles changes as a function of position. However, incontrast with the embodiment shown with respect to FIG. 6, the edges ofthe poles 710A, 710B create a jagged shape rather than a smooth one.

In both of the magnetic targets 600 and 700 of the preceding twofigures, a so-called absolute magnetic field sensor element can detectthe magnetic field in the y direction, By, along the axis y=0.Background magnetic fields, however, could be included in thismeasurement (e.g., if the sensor elements are not sufficientlyshielded). Alternatively, a gradient sensor can be used to detect thechange in By as a function of y, for example by placing one element aty=−1 mm and the other one at y=+1 mm, and calculating the differencebetween the By-fields measured by each sensor element. This gradient islarger for small y-width of the poles. In those embodiments, becausedBy/dy is differential, it is not affected by homogeneous magneticdisturbances.

The smallest y-width of all poles 610A, 610B and 710A, 710B has to belarge enough not to be degraded by mounting tolerances. If the y-play ofthe arrangement (e.g. the bearing of a movable part) is +/−1.5 mm theminimum width can be 4 mm or greater, for example. At large widths, Bychanges as a function of y only marginally, so that the system cannotdiscriminate between poles of different widths any more. Moreover, atair gap changes the By-field also changes. The system can be improved tocompute By-amplitude over Bx-amplitude or By-amplitude overBz-amplitude, yet they also change slightly. Further changes of By-fieldor By-amplitude, or changes to the ratio of By-amplitude over Bx- orBz-amplitude, can result from inaccurate y-positioning. Nominally thesensor die should be located at y=0, yet due to assembly tolerances itcan also rest e.g. at y=0.5 mm or 1 mm (or −0.5 mm or −1 mm). This alsoslightly changes the By-field. All these reasons limit the availablenumber of useful discretization steps for widths (e.g., W3-W2, W2-W1 ofFIG. 6).

A sensor with a stripe of 1 mm thickness on a steel-back with 4 mm longnorth- and south-poles in the x-direction and an air gap of 1-3 mmbetween sensor element and surface of magnet, and a y-position of thesensors between −1.5 mm-1.5 mm, can discriminate between 6 differentwidths:Ratio=0.25-0.515 for w=4 mmRatio=0.13-0.255 for w=7 mmRatio=0.039-0.126 for w=9 mmRatio=0.0067-0.0385 for w=12.5 mmRatio=0.00075-0.0063 for w=17 mmRatio=0.00007-0.00075 for w=22 mmwhereby “Ratio” is the ratio of (difference of By-amplitudes for sensorelements whose y-position differs by 2 mm) divided by (averageBx-amplitude on both sensor elements).

The embodiments described herein address many of the deficiencies ofconventional systems. In particular, a single sensor die or chip or atleast a single sensor package which might contain more than one chip isused in each of the embodiments above. This results in lower costs andhigher reliability of the overall system. Furthermore, the singledie/single package reduces costs and failure modes associated withelectromagnetic compatibility and electrostatic discharge. The singledie/single package constructions further reduce the costs and failuremodes by reducing the number of connections, wires, harnesses, discretecapacitors, and other structures. Furthermore, the single chip/singlepackage design reduces the power dissipation of the system. Embodimentscan use only a single multipole, rather than two different magnets oftenfound in conventional systems (one multi-polar and the other onedipolar). The multi-polar permanent magnet described in embodiments issimple to manufacture, because it can be a plain, relatively flatstructure. For example, in target wheels (i.e., circular magnetictargets that rotate about a center of rotation), the permanent magnetneed not be twisted out of the (r,φ)-plane. In alternative embodiments,the permanent magnetic pattern can also be applied to the outside of adrum (i.e., by attaching it to a curved (φ,z)-surface instead of theflat (r,φ)-surface). This is readily seen if the magnetic stripes ofFIGS. 6, 7 are applied to the drum surface such that they encircle thedrum fully whereby the bottom edge and the top edge (i.e. the edges withminimum and maximum x-position) coincide.

Various embodiments of systems, devices and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the invention. It should be appreciated,moreover, that the various features of the embodiments that have beendescribed may be combined in various ways to produce numerous additionalembodiments. Moreover, while various materials, dimensions, shapes,configurations and locations, etc. have been described for use withdisclosed embodiments, others besides those disclosed may be utilizedwithout exceeding the scope of the invention.

Persons of ordinary skill in the relevant arts will recognize that theinvention may comprise fewer features than illustrated in any individualembodiment described above. The embodiments described herein are notmeant to be an exhaustive presentation of the ways in which the variousfeatures of the invention may be combined. Accordingly, the embodimentsare not mutually exclusive combinations of features; rather, theinvention can comprise a combination of different individual featuresselected from different individual embodiments, as understood by personsof ordinary skill in the art. Moreover, elements described with respectto one embodiment can be implemented in other embodiments even when notdescribed in such embodiments unless otherwise noted. Although adependent claim may refer in the claims to a specific combination withone or more other claims, other embodiments can also include acombination of the dependent claim with the subject matter of each otherdependent claim or a combination of one or more features with otherdependent or independent claims. Such combinations are proposed hereinunless it is stated that a specific combination is not intended.Furthermore, it is intended also to include features of a claim in anyother independent claim even if this claim is not directly madedependent to the independent claim.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims for the present invention, it isexpressly intended that the provisions of Section 112, sixth paragraphof 35 U.S.C. are not to be invoked unless the specific terms “means for”or “step for” are recited in a claim.

What is claimed is:
 1. A position sensor comprising: a magnetic targetcomprising a magnetic multipole configured to generate a magnetic fieldcomprising, at a first region, a first component, a second component,and a third component, wherein the first, second, and third componentsare mutually perpendicular to one another at the first region andwherein the magnetic target is configured and arranged to co-rotate witha rotating component such that the first component oscillates in acourse of a rotation with a non-constant amplitude at the first region;and a sensor die comprising: a first sensor element configured tomeasure the first component at the first region; and a second sensorelement configured to measure at least one of the second and thirdcomponents substantially at the first region; and wherein the first andsecond sensor elements are mounted such that an air gap distance to apermanent magnetic ring (PMR) of the magnetic multipole is substantiallyconstant in the course of the rotation and a projection in an air gapdirection of a sensor track of the first sensor element, and aprojection in another air gap direction of a sensor track of the secondsensor element are both fully encompassed by the magnetic multipole. 2.The position sensor of claim 1, wherein the magnetic multipole comprisesa set of pole pairs, wherein the first and second sensor elements areconfigured to provide signal amplitudes to determine a global positionof the magnetic target.
 3. The position sensor of claim 1, wherein themagnetic multipole comprises a ring mounted eccentrically on a firstportion having a center of the rotation.
 4. The position sensor of claim1, wherein the magnetic multipole comprises a non-toroidal geometry. 5.The position sensor of claim 1, wherein the magnetic multipole comprisesa discontinuity.
 6. The position sensor of claim 1, wherein at least oneof the first sensor element and the second sensor element comprise agradiometric sensor system.
 7. The position sensor of claim 1, andfurther comprising a circuitry configured to: determine a firstamplitude corresponding to an output from the first sensor element;determine a second amplitude corresponding to an output from the secondsensor element; and produce a signal corresponding to the firstamplitude divided by the second amplitude.
 8. The position sensor ofclaim 7, and further comprising a third sensor element configured tomeasure at least one of the first, second and third components.
 9. Theposition sensor of claim 8, wherein: the circuitry is configured todetermine a global position based upon the signal; and the circuitry isfurther configured to determine a local position based upon an output ofthe third sensor element.
 10. The position sensor of claim 1, andfurther comprising a shielding, wherein the sensor die is arrangedbetween the shielding and the magnetic multipole.
 11. A magneticmultipole comprising: an alternating sequence of magnetic south andnorth poles arranged along a first direction arranged such that amagnetic field generated by a magnetic multipole at a first region has afirst component, a second component, and a third component, wherein thefirst, second, and third components are mutually perpendicular at thefirst region, wherein an element to mount the magnetic multipole on anaxis for a rotation around a center of the rotation; and the magneticmultipole is mounted on the element such that the first componentoscillates with an amplitude that is not uniform along a sensor trackcircle and the second component oscillates with another amplitude thatis uniform along the sensor track circle, wherein the sensor trackcircle is a circle centered to the axis of the rotation.
 12. Themagnetic multipole of claim 11, and further comprising a substrate,wherein the alternating sequence is arranged on the substrate.
 13. Themagnetic multipole of claim 11, wherein the magnetic multipole comprisesa thick portion and a thin portion.
 14. The magnetic multipole of claim11, wherein the magnetic multipole comprises a non-toroidal geometry.15. The magnetic multipole of claim 14, wherein the magnetic multipolecomprises a discontinuity.
 16. A method of determining a position of amember that is movable in a first direction, the method comprising:arranging a magnetic multipole along the first direction, the magneticmultipole comprising a plurality of magnetic poles having alternatingpolarity; arranging at least two magnetic sensor elements at a firstregion proximate to the magnetic multipole and spaced apart from themagnetic multipole in a second direction, wherein the second directionis perpendicular to the first direction; sensing a first magnetic fieldcomponent of a magnetic field of the magnetic multipole along a thirddirection, wherein the third direction is perpendicular to both thefirst and second directions at the first region to generate a firstsignal; sensing a second magnetic field component of the magnetic fieldof the magnetic multipole along a fourth direction that is perpendicularto the third direction at the first region to provide a second signal;and deriving, from the first signal, a first information that isindicative of an amplitude of a signal course of the first magneticfield component; deriving, from the second signal, a second informationthat is indicative of another amplitude of a signal course of the secondmagnetic field component; and combining the first and second informationin order to provide a global position of the member.
 17. The method ofclaim 16, and further comprising sensing a gradient of the magneticfield component along the third direction and deriving the firstinformation based on the sensed gradient.
 18. The method of claim 16,wherein: a first magnetic field strength of the magnetic multipole is asinusoidal function of the position and has a first amplitude that is astrong function of the position; and a second magnetic field strength ofthe magnetic multipole is a sinusoidal function of the position, and hasa second amplitude that is either not a function or only a weakerfunction of the position in relation to the first amplitude.
 19. Themethod of claim 16, and further comprising sensing a third magneticfield strength of the magnetic multipole corresponding to a thirdmagnetic field perpendicular to the first direction at the first region,and determining a local position based upon the third magnetic fieldstrength.